In general, an excavator operates a hydraulic pump and a pilot pump using power outputted from an engine, and a hydraulic pump discharges hydraulic oil, and provides the hydraulic oil to a plurality of control units.
Actuators are connected to the plurality of control units, respectively.
In addition, a pilot pump discharges pilot hydraulic oil to provide the pilot hydraulic oil to spools of the plurality of control units, and when a worker manipulates a joystick, pilot hydraulic oil is provided to the control unit which corresponds to the manipulation.
When the spool of the corresponding control unit is opened, the hydraulic oil is provided to a corresponding actuator, and the corresponding actuator is operated.
The plurality of actuators may include a traveling motor, a swing motor, a boom actuator, an arm actuator, a bucket actuator, and the like, and may further include an option actuator or an outrigger, or a dozer.
Hereinafter, a general excavator hydraulic circuit system will be described with reference to attached FIG. 1.
As illustrated in FIG. 1, the excavator hydraulic circuit system includes a configuration which generates hydraulic pressure of the hydraulic oil, and a control unit which controls a flow of the hydraulic oil.
The configuration in which hydraulic pressure of the hydraulic oil is generated is a configuration in which an output shaft of the engine E is connected to shafts of the first and second hydraulic pumps P1 and P2, and the pilot pump P3, and when the engine E is operated, the first and second hydraulic pumps P1 and P2 discharge the hydraulic oil, and the pilot pump P3 discharges the pilot hydraulic oil.
Meanwhile, the hydraulic oil discharged from the first hydraulic pump P1 is connected to a drain line 30 through a first bypass line 10, and the hydraulic oil discharged from the second hydraulic pump P2 is connected to the drain line 30 through a second bypass line 20.
Meanwhile, a safety line 40 is connected to outlet sides of the first and second hydraulic pumps P1 and P2, and a safety valve unit 50 is provided in the safety line 40.
When pressure generated in the hydraulic oil in the hydraulic circuit system becomes higher than allowable pressure, the safety valve unit 50 is opened to discharge the hydraulic oil.
In the first bypass line 10, a traveling control unit 100, an option control unit 110, a swing control unit 120, a second boom control unit 130b, and a first arm control unit 140a are sequentially disposed. Hereinafter, the option control unit 110, the swing control unit 120, and the second boom control unit 130b, and the first arm control unit 140a are called a first control unit group A.
In addition, an outrigger control unit 150, a bucket control unit 160, a first boom control unit 130a, and a second arm control unit 140b are sequentially disposed in the second bypass line 20. Hereinafter, the outrigger control unit 150, the bucket control unit 160, the first boom control unit 130a, and the second arm control unit 140b are called a second control unit group B.
Meanwhile, a first inlet side of the first arm control unit 140a, and an inlet side of the second arm control unit 140b are connected through a first confluence line 41.
In addition, a first parallel line 12 has one side that is connected with an outlet side of the first hydraulic pump P1, and the other side that is connected with the aforementioned first confluence line 41, and has a check valve so as to prevent a reverse flow.
In addition, a second parallel line 22 has one side that is connected with an outlet side of the second hydraulic pump P2, and the other end that is connected with a second inlet side in the second arm control unit 140b, and has a check valve to prevent a reverse flow.
The first parallel line 12 provides the hydraulic oil to the control unit that is provided in the first bypass line 10, and the second parallel line 22 provides the hydraulic oil to the control unit that is provided in the second bypass line 20.
According to the hydraulic circuit system in an excavator, which is configured as describe above, a cut off function is operated when a worker selects the traveling mode by manipulating traveling/work selection switches in the driver seat.
When the cut off function is operated, the pilot hydraulic oil is provided to the traveling control unit 100 and traveling is possible, but the pilot line of the control unit of another actuator is shut off, such that other operations, for example, upper body turning, moving a boom upward and downward, arm dump/cloud, and bucket dump/cloud other than the traveling are not performed even when a joystick is manipulated.
However, the general excavator hydraulic circuit system has the following problems.
When the engine E is operated, the first and second hydraulic pumps P1 and P2 and the pilot pump P3 are simultaneously operated, and the hydraulic oil is provided from the first hydraulic pump p1 to the traveling control unit 100.
The pilot pump P3 may be used to discharge the pilot hydraulic oil so as to control the traveling control unit 100, or control other valves.
However, there is a problem in that the hydraulic oil, which is discharged from the second hydraulic pump P2, is not utilized, but is immediately discharged.
Therefore, the engine needs to be operated with the higher number of revolutions (rpm) of the engine, for example, 2,000 rpm, that is higher than when general work is performed, in order to supply the hydraulic oil that is sufficient for traveling when the excavator travels.
That is, the number of revolutions of the engine when the excavator travels is relatively high in comparison with a case in which the number of revolutions of the engine is set to be 1,500 rpm to 1,800 rpm when general work is performed.
Therefore, in the related art, an engine having high output needs to be selected so as to output the high number of revolutions in order to satisfy traveling performance, and as a result, there is a problem in that a loss is increased when the engine is operated, and fuel efficiency deteriorates.
Meanwhile, there is difficulty in determining a capacity specification of a hydraulic pump in consideration of both traveling performance and performance of working machines.
For example, in a case in which the capacity of the traveling motor is determined in consideration of traveling performance and traction force, a traveling speed may be designed by the number of revolutions of the engine and the capacity of the hydraulic pump.
However, since the capacity of the hydraulic pump is determined depending on performance of the working machine, the number of revolutions of the engine, which satisfies the traveling speed, is inevitably determined regardless of the intention of a designer.
As a result, because there is no performance factor which may efficiently design a traveling system in order to satisfy traveling target performance (traction force and traveling speed) of the excavator, there is a problem in that efficiency of the traveling system is inevitably much lower than efficiency of the working machine.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.